Improvements in performances of MOS transistors and CMOS have been made by shrinkage or scaling down thereof, for example, shortening a channel length and a reduction in thickness of a gate insulating film. A reduction in thickness of the gate insulating film and a minimum size or dimension for process have become closer to the limitations. A further improvement in performance can not depend upon the limited shrinkage or scaling down of the device, but should depend upon any other measures than the shrinkage or scaling down of the device.
One of the improvements in performance of the device is a technique of applying a stress to a channel region for improving a carrier mobility, so called strained-Si channel technique. The followings are the technique for forming a device in an strained Si wide region. A first conventional method is that an Si epitaxial growth over a single crystal SiGe relaxed layer is made, so that an MOS is formed in the Si epitaxial layer. A second conventional method is that an extremely thin SOI is heated at a high temperature and then cooled to room temperature, and in this cooling process, a strain is generated in the SOI. This strain is utilized.
The first conventional method has problems for how to keep a surface planarity of Si layer grown over the relaxed layer as well as how to reduce defects in the related layer or the strained Si layer. The first conventional method is not practically realizable. In accordance with the first conventional method, a strain of at most 0.3 GPa can be introduced, thereby making it difficult to obtain a sufficiently high mobility.
Different from the technique for introducing the uniform strain into the wide area of the substrate, another technique is present for controlling a lattice strain of a channel or a mobility of carriers by utilizing a stress caused by the device structure or process, particularly a device isolation technique. Japanese laid-open patent publication No. 2001-28341 discloses that an Si layer is deposited by a sputtering method over an SiO2 layer, which may be compressible and is deposited over an Si substrate. Then, the Si layer is made into an Si island for subsequent heat treatment to cause a compression of the SiO2 film and a crystallization of the Si film, whereby a compressive strain is introduced into a p-channel MOS field effect transistor. Even the heat treatment is made to the Si film deposited over the amorphous SiO2 film, then the Si film is not crystallized. The compressive strain as introduced provides a mobility of polycrystalline. This is unsuitable for the cases that the MOS transistor or the CMOS is formed over the single crystal Si.
Japanese laid-open patent publication No. 2000-36567 discloses that a thickness of an oxide film buried in an SOI wafer and a condition for forming a field oxide film for forming an island of the Si film over the SOI wafer are properly set to allow the Si island to accept the compressive stress. A gate delay time of the p-channel MOS field effect transistor in accordance with this method is smaller than that of the p-channel MOS field effect transistor formed over a bulk Si substrate. An increase in a mobility of holes is confirmed. Since the strain introduced into the island is the compressive strain, the increase in the mobility is the opposite effect to the n-channel MOS field effect transistor. For this reason, it is not anticipated to improve the performance of CMOS.
Japanese laid-open patent publication No. 11-54756 discloses that each mobility of electron and hole in biaxial-compressive-and-tensile-strained Si are calculated to investigate what strain is effective to improve the performance of CMOS. As a result of the investigation, it was confirmed that the compressive strain of 1%–2% improves electron and hole mobilities. An Si island structure was proposed for realizing the strained Si, wherein the structure comprises an SOI isolated in LOCOS method. The strain of 1%–2% is to generate crystal defect and break Si crystal. Practical realization of this conventional method is difficult.
An issue of the present invention is to solve the above-described problems with the prior art.
An object of the present invention is to improve an ON-current of a p-channel MOS field effect transistor and an n-channel MOS field effect transistor for controlling a strain of a channel region, wherein a stress caused by a device structure is controlled by a method highly matched to the conventional process as well as to provide a CMOS comprising an n-channel MOS field effect transistor and a p-channel MOS field effect transistor which are improved in ON-current.